/Engine/Plugins/Runtime/MassEntity/Source/MassEntity/Public/MassObserverRegistry.h
void RegisterObserver ( const [UScriptStruct](API\Runtime\CoreUObject\UObject\UScriptStruct) & ObservedType, const [EMassObservedOperation](API\Plugins\MassEntity\EMassObservedOperation) Operation, [TSubclassOf](API\Runtime\CoreUObject\Templates\TSubclassOf)< [UMassProcessor](API\Plugins\MassEntity\UMassProcessor) > ObserverClass )